A known method for forming a plated coating on an inner circumferential wall of a cylinder is a high-speed plating method in which a plated coating is formed on an inner circumferential wall of a cylinder at a high speed by the forced flow of a plating liquid along the inner circumferential wall of the cylinder (e.g., JP-A-07-118891).
The conventional plating apparatus and plated coating formed by this apparatus are described in reference to FIGS. 12, 13a, and 13B.
In FIG. 12, a support block 202 is attached to a stand 201 of a plating apparatus 200, and a cylindrical electrode 203 is attached to the support block 202. In this condition, an outflow channel 205 for the cylindrical electrode 203 and an outflow channel 204 for the support block 202 are arranged concentrically.
A cylinder block 207 is placed on the support block 202 in a condition whereby the block has been inverted top to bottom (e.g., in a condition in which the crankcase 208 is upwards), and the cylindrical electrode 203 is disposed inside the cylinder 209.
A channel 211 is formed in the gap between an inner circumferential wall 209a of the cylinder 209 and the cylindrical electrode 203. The channel 211 connects with an introduction channel 212 of the support block 202.
An opening 209b of the cylinder 209 (opening on the side of the crank shaft) is closed off with a lid 214. A bottom end of a rod 215 is connected to this lid 214, and the rod 215 extends upwards. An upper end of the rod 215 is supported by a support plate 216. The support plate 216 is a member that is carried on the upper end of the cylinder block 207.
By supplying a plating liquid to the introduction channel 212 in this condition, the plating liquid is caused to flow from the introduction channel 212 as indicated by the arrow A into the channel 211 between the cylindrical electrode 203 and the inner circumferential wall 209a of the cylinder 209.
The plating liquid that reaches the upper end portion of the cylindrical electrode 203 is guided by the lid 214 and caused to flow into the outflow channel 205 in the cylindrical electrode 203 as indicated by the arrow B. The liquid then flows from the outflow channel 205 into the outflow channel 204 of the support block 203 as indicated by the arrow C.
In this manner, the plating liquid is forced to flow along the inner circumferential wall 209a of the cylinder 209, thereby rapidly forming a plated coating 218 on the inner circumferential wall 209a (refer to FIG. 13A).
The gap between the cylindrical electrode 203 and the inner circumferential wall of the cylinder 209, i.e., the channel 211, is formed as a cylinder which is comparatively narrow. Consequently, when the plating liquid is supplied to the cylindrical channel 211 as indicated by the arrow A, the plating liquid does not easily flow uniformly throughout the interior of the cylindrical channel 211. For this reason, a uniform plated coating 218 is difficult to form on the inner circumferential wall 209a of the cylinder 209, and increases in productivity are impeded, leaving room for improvement.
The plated coating formed by the aforementioned high-speed plating apparatus will be described next.
In FIG. 13A, the cylinder 209 is closed off by an external circumferential part 214a when the lid 214 seals the inner circumferential wall 209a of the cylinder 209. Thus, the plating liquid that flows along the inner circumferential wall 209a of the cylinder 209 up to the upper end 203a of the cylindrical electrode 203 strikes the lid 214 and enters into the outflow channel 205 in the cylindrical electrode 203 as indicated by the arrow B.
For this reason, the plating liquid is stirred comparatively effectively in the vicinity of the external circumferential part 214a of the lid 214. Thus, the plated coating 218 assumes a condition in which the coating runs along the outer circumferential part 214a of the lid 214 and protrudes towards the center of the cylinder 209, thereby forming flash 218b at the boundary 218a of the plated coating 218.
In FIG. 13B, the surface of the plated coating 218 is honed to the finished surface position 221 indicated by the broken line, and the inside diameter of the plated coating 218 (i.e., the inside diameter of the cylinder 209) is formed at the prescribed size.
Because flash 218b is formed at the boundary 218a of the plated coating 218, an excessive load is placed on the flash 218b during honing. Consequently, there is the danger that the plated coating 218 will separate from the inner circumferential surface 209a at the boundary 218a, which is an impediment to productivity increase.
The plating apparatus 200 shown in FIG. 12 has, as essential members, a support plate 216, a rod 215, and a lid 214, whereby the opening 209b of the cylinder 209 is closed off by the lid 214.
Moreover, regarding the outer circumferential part 214a of the lid 214 (refer to FIG. 13A), an O-ring (not shown in the figures) is necessarily provided on the outer circumferential part 214a of the lid 214 in order to seal the inner circumferential wall 209a of the cylinder 209. In addition, the structure of the lid 214 is complicated because the bottom end of the rod 215 is attached to the lid 214.
Moreover, the rod 215 must extend to the upper end of the cylinder block 207, and the rod 215 is therefore comparatively long. Moreover, the support plate 216 is made comparatively large so that the support plate 216 that supports the upper end of the rod 215 can be placed on the top end of the cylinder block 207.
For this reason, the plating apparatus 200 has a large number of parts, and the plating apparatus 200 is also large. Consequently, reduction in equipment costs is difficult to achieve.
In addition, when the opening 209b of the cylinder 209 is closed by the lid 214, the lid 214 must be moved from the upper opening 219 of the cylinder block 207 to the opening 209b of the cylinder 209. Consequently, it is not possible to use the plating apparatus 200 for workpieces that do not have an upper opening 219 as with the cylinder block 207 (e.g., a cylinder block with an integrated cylinder head).
Specifically, with the plating apparatus 200, utilization is restricted based on workpiece shape, and thus there is room for improvement in this regard.